Synthetic amphiphilic macromolecules composed of stearic acid covalently linked to fluorescent dextran derivatives were synthesized as models for membrane proteins. These water-soluble molecules adsorb to all artificial and cell membranes tested. The lateral diffusion and qualitative behavior of these molecules on the surface of fibroblasts have been studied and artificial membranes. The lateral diffusion constant of these molecules on the surface of fibroblasts is about 2 times 10 to the minus 10th power sq. cm./sec, and on synthetic membranes is about 5-fold faster. Addition of antibody to determinants on the dextran produces patching for all membrane bound molecules; for lymphocytes and for many fibroblasts, capping also occurs. In addition the technology developed was used to allow the formation of IgA coated erythrocytes which have successfully detected IgA specific Fc receptors on mouse lymphocytes.